Control of Asymmetry 473 



symmetrical to asymmetrical chelae. In this asymmetry the 

 crusher occurs as frequently on one side of the body as on the 

 other. 



PLAN AND METHOD OF THE EXPERIMENTS 



The present experiments were made in the following stages of 

 the lobster's development — the stages being designated as first, 

 second, etc., according to the number of moults since the time of 

 hatching: 



The second larval stage; 



Fourth stage ; 



Fifth stage; 



Twelfth stage or lobsters a year old ; 



Adult lobsters. 

 All of these experiments attempt to determine to what extent 

 asymmetrical differentiation of the chelae can be controlled by 

 amputation. In lobsters, as is well known, an injured limb is 

 thrown off spontaneously or autotomously, separating along a cer- 

 tain "breaking plane" near the basal joint. 



It was found necessary to exercise great care in the mutilation 

 and rearing of the delicate larval lobsters. The chela was 

 removed, under a small hand lens when necessary, by grasping 

 the tip of the limb with a pair of forceps. In the older lobsters 

 the chela promptly separates at the breaking plane. In the 

 younger lobsters however the separation is not so readily obtained 

 and a gentle pull may be required. The most difficult period in 

 which to keep the lobsters alive is during the second and third 

 stages. After several failures with ordinary aquaria the best 

 results were obtained by keeping the animals in a current of fresh 

 sea-water. This was accomplished by means of a rather elaborate 

 apparatus built in the pool of a wooden float. The bottoms of 

 pulp pails were removed and replaced by "bobbinet" cloth with 

 meshes small enough to prevent the escape of the lobsters. A 

 second cover, or false bottom, of mosquito bar was also found 

 necessary — not to confine the lobsters but to prevent the ever 

 present shrimp from pulling them out through the meshes. 

 These pails were then suspended in the water of the pool. In 



